Projection images of a body are used for generating tomography images. The projection images may be generated by a projection device, for example a computer tomograph (CT). The body may be a human, animal, or an object. A volume model of at least part of the body is formed on the basis of the projection images. A sectional view of the volume model represents a tomography image or a tomogram.
If there is a metal object in the body, for example a metal clip, the volume model may include metal artifacts. Individual voxels (volume elements) of the volume model in the immediate vicinity of the metal object do not describe the property of the body tissue located there but may be, depending on overexposure or underexposure, have voxel values that are very similar to the voxel values of the metal object. The individual voxels may not be distinguishable.
A scientific publication by Veldkamp et al. (W. J. H. Veldkamp, R. m. S. Joemai, A. J. van der Molen, J. Geleijns, “Development and validation of segmentation and interpolation techniques in sinograms for metal artifact suppression in CT”, Medical Physics 37, 620 (2010)) discloses a method for reducing metal artifacts.
The form of the metal object may be determined by using the method or by manual marking the metal object in a tomography image. The form may be considered when calculating a volume model. The effect of the metal object on the voxels in the vicinity is reduced in the volume model.